This type of horn is described in the document FRA-2 069 792.
By virtue of its design, the loud horn heats up when it operates.
In effect, a temperature increase, provoked by the electromagnetic generator, inside the volume of the housing closed by the diaphragm results in an increase of the internal pressure.
This is why in the above-mentioned document a respiration hole has been provided so as to facilitate exchanges with the outside and enabling the external and internal pressures to be balanced.
This hole may be calibrated and itself form means for protection against water penetration.
In one variant, it is possible to add to the hole a filter protecting the horn from water penetrating.
This hole is embodied for one portion formed by injecting plastic material into the housing, protection being provided by a sheath or tube.
In one variant, the skirt of the housing extends outwardly by a tube overlapped by a protection cap.
All these dispositions complicate the production of the housing and in certain cases are not optimal as the holes may become clogged.
In addition, this results in embodying projections which may encumber implantation of the loud horn.
Moreover, prior to mounting, this increases risks of damage occuring to the horn by incorrect handlings.
So as to protect the respiration hole of the horn, the document FR-A-2 279 187 concerns providing an external cap which communicates with the outer atmosphere via a labyrinth hole.
The document FR-A-1 335 125 concerns an orifice to be inserted which opens into the air at a location protected from external sprayings by means of a wall forming a screen.